Why Does Water Rise – Science Experiment

A candle and some rising colored water reveal a hidden property of air that’s around you all the time.

Why Does Water Rise: The Candle Cup Water Rise Experiment
A candle and some rising-colored water will reveal a hidden property of air that’s all around you — all the time.
Candle Science and Water Level Equalization
This fun candle in water experiment will teach you a cool lesson about water level equalization. Watch closely and use everything you know about air pressure differences to explain the mystery of the rising water in this fascinating yet easy-to-perform candle experiment that will teach you important principles of air. Look for clues that explain why the water rises into the container. It may not be what you think it is, so keep your eyes open as you collect the data in this rising water experiment. The best part is that you’ll likely have to do this candle experiment several times to confirm how air pressure is involved!

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Experiment Materials

Experiment Videos

Experiment

1

Add 2-3 drops of food coloring to the water. This will make the movement of the water easier to see later. It’s interesting to watch how the drops of coloring spread through the water before stirring it.

2

Pour the colored water into the plate. You want about a half-inch (1 cm) deep puddle in the plate. More is OK.

3

Set the candle straight up in the puddle in the center of the plate. To make sure everything will fit, place the slender container over the candle and into the water. Make sure its base is well above the candle wick and its top edge is submerged under the water. Add water if needed. When you’re happy with the setup, remove the container.

4

When the candle is stable, the water is calm, and an adult is present, light the candle. The candle flame needs to burn brightly.

5

There’s no need to rush this Step; there’s a lot to watch anyway. Turn the container over again and lower it over the burning candle. Place the container on the plate in the water and let go but don’t take your eyes off of the water level inside it. You may see bubbles coming from inside the container. At first, the candle stays burning and the water level rises slowly. About the time the candle goes out, the water rises quickly. This is the mystery: why does it rise?

Repeat the procedure several times so that you can write or draw an explanation as to why the water rises. HINT: The difference in air pressure inside and outside the container is important.

How Does It Work

A common misconception in this candle in a jar experiment is that the consumption of oxygen by the flame in the container is a factor in the water rising. There may be a slight possibility that there would be a tiny rise in the water from the flame using up oxygen, but it’s extremely small compared to the actual reason. Simply put, the water would rise imperceptibly at a steady rate as the oxygen levels were consumed. You likely saw the level rise almost all at once — and pretty much after the candle’s flame went out.
What Happened in the Candle Experiment?
At first, the flame heats the air inside the container; this hot air expands quickly. Some of the expanding air escapes from under the glass or jar. (You might have seen some bubbles.) When the flame fades and goes out, the air in the container cools. The cooler air then contracts and takes up less space. That contraction creates a weak vacuum, or a lower pressure, in the container. Where’s the higher pressure? Right! It’s outside the container pressing down on the water in the dish. The outside air pushes water into the container until the pressure is equalized both inside and outside of the container — an amazing visual on water pressure equalization! The water stops rising when that pressure equalization is reached.
Practice Safe Science
In this rising water experiment, you got to see firsthand the effects of water pressure equalization and the different effects of hot air and cool air. This candle science experiment is easy to perform; however, it requires the supervision of a responsible adult — always! Ask a parent or a teacher for help when performing this candle in water experiment, or any science experiment that uses a candle or a flame to teach you an important principle of science. Looking for other amazing science experiments, like our rising water experiment? Check out our other online science experiments for kids in the Steve Spangler Science library of super-fun experiments that are great for home, school and STEM club! From all-in-one science kits and lab supplies to at-home experiments and science fair ideas, Steve Spangler Science is your top go-to for amazing science and hands-on learning!